Growers are asking how the unusually warm spring weather – and freezing nights – may affect alfalfa growth. So Dan Undersander has put together answers to those queries.

“Alfalfa is tolerant of cold temperatures,” says the University of Wisconsin Extension forage specialist. “To make the best management decision, we must understand the growth and biology of alfalfa.”

He suggests that farmers keep the following principles in mind:

• Temperatures in the 25-30ºF range, when alfalfa leaves are in early development stages, may cause leaf deformation. Leaves developed before or after such temperatures hit won’t be affected.

• Nighttime temperatures must fall to 24ºF or lower for four or more hoursto freeze alfalfa topgrowth. Temperatures at or just below freezing (28-32ºF) will not damage alfalfa. “In fact,” he adds, “we can actually have snow with no damage to growing alfalfa.”

• The only way to tell if alfalfa is damaged after a cold night is to wait two to four days to determine if leaves are wilted or blackened. If no damage is present, there is no frost injury. Damage will occur mainly to the top of the alfalfa growth, since that is most exposed to cold temperatures.

• If leaf edges only are blackened or show signs of “burn,” damage is minimal with little to no yield loss and nothing should be done.

• If only a few entire leaves on each stem are damaged but not the bud, yield loss will be minimal and nothing should be done.

• If the entire stem top – some leaves and bud – is wilted and turns brown, then the growing point, or bud, has been killed and that stem will not grow any further except from axillary shoots that may develop at leaf junctures on the stem. The plant has not been killed and new growth will occur from developing crown buds. When entire tops are frosted, significant yield loss will occur.

If frozen stems are too short to harvest, do nothing and new shoots will develop from crown and axillary buds. Yield will be reduced and harvest will be delayed while the new shoots develop.

If frozen stems are sufficiently tall to be economic to harvest (14” or more), do so.There will be no toxin in the frozen topgrowth, and it will provide good, high-quality forage. Mow immediately and harvest as normal. Regrowth will be slow and some total-season yield loss will occur. After harvest, ensure that soil fertility is adequate for good regrowth. Letting the next cutting grow to first flower will improve stand condition.

The early spring has allowed extraordinarily early alfalfa growth and, in the absence of frost damage, most farmers should be prepared to harvest dairy-quality haylage before the end of April, says Undersander. The recommendation is to cut by height using a forage quality stick for high-quality forage.